This invention relates to a metal dowel for anchorage in thin wall panels, especially plasterboard panels.
Metal dowels of this type are typically made from thin sheet steel and essentially comprise two expanding legs pressed flat together, which are configured at one end such that they taper to a point and at the opposite end, the head end, are fixedly joined together. The head end is further provided with a thread region for the screwing in of sheet metal screws or wood screws. Following the thread region, a recess is provided in the expanding legs, the edges of the recess located adjacent the thread region being formed out in a funnel shape to ensure receipt of the tip of the screw.
A metal dowel of this type is known from EP 0 274 816 B1, in which the expanding legs are joined together at the head end by a threaded head plate and protrude from this at a right angle. The metal dowel is driven into a plasterboard panel by means of a hammer, the tips of the legs being to the fore, until the head plate rests against the panel's surface. A screw is then screwed into the thread region of the head plate with the tip of the screw being guided between the expanding legs by the funnel-shaped region at the end of the recess, the expanding legs being forced apart to the point where they become anchored on the back side of the panel.
To ensure that the legs, lying flat one upon the other, stay together while being driven into the panel, a small tab or bar that protrudes from one surface of one leg is forced into a corresponding recess in the other leg, such that there is a temporary connection between the two legs. This is sufficient to hold the legs together as they are driven into the panel. As soon, however, as a sheet metal screw is screwed in between the legs, the tab or bar is pulled out of the recess and the legs are then able to expand as a result of a further screwing in of the screw to produce the desired anchorage.
In the case of this metal dowel, however, one drawback is that the head plate projects over the wall panel by approximately three times the panel's thickness and consequently remains visible when wall hooks are screwed in. In addition, the tab connection between the clamping legs functions only when there is a relatively short leg length. Thus these dowels can only successfully be used in the case of relatively thin plasterboard panels. In the case of thicker or even doubled-up panels on the other hand, where longer expanding legs are required, there is often the risk of the tips of the legs, despite the tab connection, being pushed apart as they are being driven into the panel. In this event, fragments of plaster can break off from the plasterboard panel, so that the anchorage region no longer has the strength necessary to bear the legs of the dowel.
An object of the present invention therefore is to design the above-described metal dowel such that the head end is prevented from jutting out over the surface of the wall panel and the tips of the legs, even in the case of relatively long leg lengths, are held together with absolute reliability as they are being driven into a wall panel. Better screw guidance in the entry between the expanding legs is also desired.